I have domains that average 1 unique/day, but average $.40/unique. So, the income works out to $.40/day or $145/yr. Well worth renewing.
I have another domain that get 5u/day, but it averages $.003/unique. That works out to $.015/day or $5.50/yr. Not worth renewing, unless I believe that I can find a better, more profitable use for the traffic. Most of my income is coming from PPC Services. See
www.PPCIncome.com